Nanocomposites are polymer systems containing inorganic particles with at least one dimension in the nanometer range. Some examples of these are disclosed in U.S. Pat. Nos. 6,060,549, 6,103,817, 6,034,164, 5,973,053, 5,936,023, 5,883,173, 5,807,629, 5,665,183, 5,576,373, and 5,576,372. A common type of inorganic particle used in nanocomposites are phyllosilicates, an inorganic substance from the general class of so called “nano-clays” or “clays”. Ideally, intercalation should take place in the nanocomposite, wherein the polymer inserts into the space or gallery between the clay surfaces. Ultimately, it is desirable to have exfoliation, wherein the polymer is fully dispersed with the individual nanometer-size clay platelets. Due to the general enhancement in air barrier qualities of various polymer blends when clays are present, there is a desire to have a nanocomposite with low air permeability; especially a dynamically vulcanized thermoplastic nanocomposite such as used in the manufacture of tires.
Dynamically vulcanized thermoplastic compositions comprising a polyamide and various types of elastomers are known. See, for example, U.S. Pat. No. 4,173,556; U.S. Pat. No. 4,197,379; U.S. Pat. No. 4,207,404; U.S. Pat. No. 4,297,453; U.S. Pat. No. 4,338,413; U. 4,348,502; U.S. Pat. No. 4,419,499, and U.S. Pat. No. 6,028,147. The term “dynamic vulcanization” is used herein to mean a vulcanization process in which the components of the blend are vulcanized under conditions of high shear. As a result, the vulcanizable elastomer is simultaneously crosslinked and dispersed as fine particles of a “micro gel” within the resin matrix.
Dynamic vulcanization is effected by mixing, for example, an elastomer and a thermoplastic, at a temperature which is at or above the curing temperature of the polymer in equipment to provide high shear such as roll mills, Banbury™ mixers, continuous mixers, kneaders or mixing extruders, extruders. One unique characteristic of the dynamically cured compositions is that, notwithstanding the fact that the polymer component may be fully cured, the compositions can be processed and reprocessed by conventional rubber processing techniques such as extrusion, injection molding, compression molding, etc. Scrap or flashing can be salvaged and reprocessed.
It is known to utilize exfoliated-clay filled nylon as a high impact plastic matrix, such as disclosed in U.S. Pat. No. 6,060,549 to Li et al. In particular, Li et al. disclose a blend of a thermoplastic resin such as nylon and a copolymer of a C4 to C7 isomonoolefin and a para-methylstyrene and a para-(halomethylstyrene), the blend also including nylon containing exfoliated-clays that are used as a high impact material. Further, Japanese Unexamined Application P2000-160024 to Yuichi et al. discloses a thermoplastic elastomer composition which can be used as an air barrier. The nanocomposite in Yuichi et al. includes is blend similar to that disclosed in Li et al. Other disclosures include U.S. Pat. No. 6,036,765 and EP 1 055 706 A.
There is still a problem of achieving a nanocomposite suitable for an air barrier, in particular, an air barrier incorporating the copolymer of a C4 to C7 isomonoolefin and a para-methylstyrene and a para-(halomethylstyrene). While enhancing the impact properties and abrasion resistance of plastics such as polyamides, this copolymer tends to be a poor air barrier as compared with that of polyamide alone or other low-permeability plastic matrices. What is needed is a blend of a thermoplastic resin such as nylon with the copolymer to form a nanocomposite suitable as an air barrier.